RE: Select fin for isonic
Just sliding in at the bottom of this discussion...
The 37cm is a very good and useful size on the iS101, definitely a good (and simple) option to power up your setup in "marginal" 34cm conditions, (without going the full jump to a 40 etc, with inherent extra drag etc) -or to pull out a bit more upwind if that helps in your usage.
It's also a good "small"(powered..) fin for moderate big (~7.5m*)iS101 race sails...
..other than 34, 37 is the most common size in my 101.
Cheers ~ Ian
(*92kg - so as 02b says, your mileage may vary !!)